This application claims the priority of German patent document 100 28 133.8, filed Jun. 7, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for humidifying a gas flow and to a method for using such a device.
European patent document EP 0,629,014 B1 discloses a method for humidifying process gas for the operation of fuel cells, in which finely atomized water is sprayed in a predetermined quantity, with the aid of a spray nozzle, from a supply line into a gas feed line of the fuel cell. In this method, a desired amount of water to be supplied is determined as a function of operating parameters, and is metered exactly by means of a control arrangement in such a way that the desired humidity of the process gases is established.
In this case, the water is atomized by means of a spray nozzle so that it can be supplied directly to the gas flow. Owing to the geometry of the gas-carrying passages of the fuel cell, however, the maximum permissible droplet size must be determined so that the droplets cannot block any cross sections in the area of the fuel cell. Thus, the fuel cell system must be specifically adapted to the atomization; and the outlay involved in regulating or determining the desired values for controlling the water metering is also highly complex.
In addition to direct spraying of water into the gas flows, other known devices and methods for humidifying gas flows utilize various types of membranes which separate the gas flow from a liquid flow or a liquid reservoir. The membranes allow liquid particles to enter the gas flow through the membrane and to be picked up and carried along by the gas flow. One example of such systems which can be mentioned is U.S. Pat. No. 4,973,530.
The known devices for humidifying process gases such as air or hydrogen are usually large and heavy. The media generally have to be cooled before they enter the humidifier. On the other hand, if a medium freezes in the humidifier, the humidifier is damaged.
The object of the invention is to provide a method and apparatus which achieve a high humidity or high relative humidity in a gas flow while reducing the outlay in terms of control and the device for humidifying the gas flows, and which are suitable for use at low temperatures.
This and other objects and advantages are achieved by the humidifying method and apparatus according to the invention, which includes means for atomizing a liquid into a gas feed line and means for heating the liquid. The atomizing means is provided in a spray chamber, with a heat-exchanger region for at least partially evaporating the liquid being arranged adjacent to the spray chamber. The heat-exchanger region has a multiplicity of flow passages for gas flows which are to be humidified, which flow passages are at least partially delimited by heat-exchanger surfaces for condensing and evaporating the liquid.
The invention makes it possible to carry out humidification by evaporation at low temperatures through the direct conduction of heat, without complex process controls. A further advantage of the invention is that the medium to be evaporated is very finely and uniformly dispersed in a humidifier, making the evaporation process more efficient. The device can operate both with high-temperature media and, without problems, at the freezing point. The pressure loss in the device is advantageously low.